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Nov. 7, 1961 JULIE 3,008,111

INFINITE RESOLUTION POTENTIOMETER Filed Oct. 15, 1958 INVENTOR. LOE BEJU LIE BY BLAIR, SPENCER s BUCKLES ATTORNEYS.

United States Patent Dfifice 3,008,111 Patented Nov. 7, 1961 3,008,111INFINITE RESOLUTION POTENTIOMETER Loebe Julie, Julie Research Labs.Inc., 603 W. 130th St., New York 27, NY. Filed Oct. 13, 1958, Ser. No.766,947 11 Claims. (Cl. 338-202) This invention relates to improvementsin variable resistance devices, and more particularly to means forproviding finer gradations of resistance variation over any desiredrange. The invention is particularly useful in the manufacture ofprecision potentiometers for use in modern electronic devices orsystems, as for example in precision control systems or analoguecomputers.

In the precision electrical arts, variable potential dividers areemployed for many purposes, as for example to derive a voltage whichvaries in accordance with the angular rotation of a shaft, or togenerate a voltage of a preselected wave form, or corresponding to aparticular mathematical function, in response to mechanical shaftmotion. The demand for greater precision in elec-" trical computers orcontrol devices has required the manufacture of potentiometers toprecise tolerances. For many practical considerations which arerecognized in the art, the most uniform precision production ofpotentiometers has been of the wire-wound type in which a preciselydrawn resistance wire is wound in uniformly spaced turns on a suitableinsulating support and an electrical contactor is provided for movementover successive turns to select the desired amount of resistanceincluded in an electrical circuit (or more frequently to tap a desiredpotential proportional to the contactor movement).

A long recognized problem in this art has been that of making a suitablemoving contact to the resistance coil, and of effecting smooth oruniform changes in resistance as the contactor is moved over the coilturns. This problem is particularly acute in very high resistanceotentiometers where the resistance of each turn of wire may be quitesubstantial, thus giving rise to abrupt changes or jumps in resistancevalue as the sliding contact advances from one turn to thenext. Suchabrupt changes give rise to undesirable noise when the potentiometers ofthe prior art are employed as variable voltage means in communication orcomputer circuitry. To cope with this problem various ingenious schemeshave been devised, including means for moving a sliding contactorthrough a helical path in constant engagement with but a single turn ofhelically wound resistance wire. Another proposal has been to employ twoor more rotatable drums in combination with a gear drive and means forunwinding a strand of resistance wire from one drum simultaneously withwinding it upon another, and making electrical contact to the strand asit is being wound. All such prior art devices have been costly andcumbersome, in addition to posing maintenance problems due to theirsusceptibility to mechanical failure.

Accordingly, a principal object of the present invention is to overcomethe disadvantages of the prior art by providing a potentiometer havingsubstantially infinite resolution of resistance variation over anydesired range of resistance. A further object is to provide asubstantially noise-free variable potential device. Another ob ject isot provide such improved resolution and noisefree operation in a morecompact physical form of construction for potentiometers. Another objectis to provide a more economical form of construction for high precisionpotentiometers. An additional object is to provide all of the advantagesabove mentioned in a simple but rugged potentiometer device capable oflong life and reliable operation. Other objects of the invention will inpart be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction,combinations of elements, and arrangements of parts, which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the inventionreference should be had to the following description taken in connectionwith the accompanying drawing in which like references designatecorresponding parts in the several figures.

FIGURE 1 is a perspective view of a a cylindrical wire-woundpotentiometer employing a rotatable wiper arm in accordance with theinvention;

FIGURE 2 is an enlarged view of the contacting portion of the wiper armof FIGURE 1 and showing the resistance element in the contactor portionthereof;

FIGURE 3 illustrates an alternative embodiment of the invention asadapted to a linear potentiometer construction;

FIGURE 4 is an enlarged structural schematic view showing in greaterdetail the manner in which the distributive resistance wiper element ofthe movable contactor engages a plurality of fixed turns of resistanceWire in the potentiometer construction according to the invention; and

FIGURE 5 is an electrical schematic diagram useful in illustrating theoperation of the invention.

The invention may be employed in any type of variable resistance ortapped potential device which employs a movable contactor. The precisionbenefits of the invention derive from my use of a distributive contactof relatively high electrical resistivity. Thus the contactor of myinvention serves as a homogeneous interpolating device between the turnsof the main potentiometer winding. According to one embodiment theresistive contact material may extend along the exposed turns of themain winding with negligible depth, while in another embodiment theresistive material of the contacting surface may have appreciable depth.In both of these embodiments the electrical connection to the resistiveslider is made to the center of the contact material, on the contactorface opposite the main winding engaging surface. By virtue of thehomogeneous resistance of the contactor, the resistance or voltagecontribution of the main winding points to the tapped potential at theslider connection point are averaged. Thus the invention provides avariable potential divider capable of producing a monotonic function ofvoltage variation with physical movement of the variable member.

Referring now to FIGURE 1 of the drawings, a cylindrical potentiometerindicated generally at 10 includes a wire-wound resistance element 12comprising a strand of resistance wire 14 wound upon an insulating card16 and enclosed within an insulated casing 18. Opposite ends ofresistance wire 14 are secured to external terminals 20 and 22 in aconventional manner. A rotatable shaft 24 extends normally through thecasing 18, through a conventional bushing. Affixed to the inner end 26of shaft 24 is a rotatable wiper arm 28 which in this embodiment isformed of insulating material. The radiallydisposed end 30 of rotatablearm 28 carries on its under surface, in conductive engagement with theexposed surfaces of resistance wire 14, a resistance element 32 whichmay either be formed of a separate winding upon the insulated arm 28 ormay be composed of a substantially homogeneous resistance material aswill be described more fully in reference to FIGURE 2. At a centralpoint 34 on Wiper resistance element 32, electrical connection is madeby conductor 36, the opposite end of which may be connected to the shaftend 26 and/or to a metallic wiper arm 38 in conductive engagement withthe flat surface of metallic collar 40. Collar 40 is connected by aconductive strap 42 to an external center tap terminal 44. Thus acontinuous conductive path through conductors 36, 38, and 42 serves tomaintain terminal 44 constantly at the potential of mid-point 34- on theresistive wiper element 32. The manner in which this structure operatesto provide monotonic voltage functions will be described more fullyhereinafter with reference to FIGURE 4 and FIGURE 5.

Referring now to FIGURE 2, the details of the resistive Wiper contactmay be more clearly seen as follows: The resistive portion of the wipercontact element 32 may be formed of a helically wound resistance wireembedded in a suitable insulating material 33, as for example an epoxyresin, with the surface portions of each turn lying in a common planebeing bared for engagement with the main potentiometer winding; or theresistance portion 32 of the wiper arm may be formed of a film typeresistance material as for example rhodium, beryllium, titanium,chromium, or of an alloy including any desired combination of theseelements. Alternatively, resistive portion 3 2 may be formed of selectedcarbon compounds, as for example boron-carbon, or pyrolytic-carbon. Itis preferable that the total distributive resistance of the wiperresistive element 32 should bear a predetermined relation to theresistance of the main wiper turns with which the surface of resistiveelement 32 is normally in conductive engagement. Preferably the totaldistributed resistance of element '32 should be at least twice theresist-ance of the corresponding winding turns with which element 32 isin engagement when the wiper arm is assembled in the structure shown inFIGURE 1.

Reference is now made to FIGURE 3 of the drawings which discloses analternative structural embodiment wherein the main body of theresistance comprises a helically wound resistance coil 50, mounted uponan insulating rod or drum 52 which may be mounted upon a suitable 'base53 by means of brackets 54 and 55. Opposite ends 56 and 58 of theresistance coil may be secured to drum 52 by means of clamps 60 and 62by which connections may be made to an external potential source.Vertical supports 64 and 65 secured to base 53 may hold a longitudinalslider carrying rod 66 substantially parallel to the axis of resistancedrum 62. Rod 66 supports and guides a movable slider member generallyindicated at 68 which comprises an insulated slider handle 70 to whichis afiixed by means of compression springs 72-72 a resistive contactmember 74 having a substantially homogeneous, uniformly distributedresistance. A slider tap connection made by conductor 76 to the centralpoint '78 of resistive slider element 74 completes the electricalconnections for this embodiment of the invention. It will be apparent,of course, that slider connection.- 76 may be brought out loosely asshown in FIGURE 3 or that suitable means, as for example, aPhosphor-bronze spring slider arrangement may be employed to establishthis connection with slider guiding rod 66 if desired. The distributiveresistance element 74 in the embodiment of FIGURE 3 may be formed of anyof the materials discussed above in reference to the construction ofresistive element 32 as described in FIGURE 2, or resistive slidingcontactor 74 may be formed of a suitable carbon compound.

Referring now to FIGURE 4 which is a structural schematic diagram, itwill be seen that the resistive wiper element 32 conductively engages aplurality (as shown 3) of resistance turns on the main potentiometerwinding 14. For effective operation the wiper contactor must alwaysengage at least two turns of the main potentiometer winding 14, andpreferably the movable resistance Wiper element should engage three ormore turns of winding 14. Ideally the total distributed resistance ofwiper element 32 should at least equal or substantially exceed the totalresistance of the maximum number of potentiometer winding turns engaged.A minimum resistance ratio of 2:1 has been found satisfactory for mostpurposes.

4; Referring now to FIGURE 5, which is an electrical schematic diagramof a potential divider according to the invention, the manner in whichthe invention operates to achieve noise free uniform monotonic functionswill be readily understood. As seen in FIGURE 5, the slider contactor 32always engages at least two contacts on the potentiometer winding 14.For purposes of illustration in this fimlre the engaging points on theresistance winding are designated as separate taps (which in effect theyare on a wire-wound potentiometer) and three taps (here designated l, 2,and 3) are shown in engagement with the contacting surface of resistancewiper element 32. As the slider 32 is advanced along the winding in thedirection show-n by the arrow in FIGURE 5 the resistance between eitherend of the potentiometer winding 14 and the slider connection 36 doesnot vary abruptly by an amount equal to the total resistance betweeneach tap (or turn of the winding) but the resistance changes graduallyand uniformly with each incremental motion of the resistance slider 32,thus producing monotonic voltage functions.

The total resistance between opposite ends of the slider element 32should preferably exceed the total resistance between two adjacent turnsor tapped points of the potentiometer winding by a substantial amount(of the order of 2 to 1 or more). As the slider moves from left to rightas indicated by the arrow in FIGURE 5, the slider resistance portion abetween the center tap c and contact point 1 increases simultaneouslywith decreasing resistance of portion b between center tap c and contactpoint 2, until 0 is in direct engagement with 2. As motion of slider 32continues in the same left-to-right direction, the resistance portion abecomes disengaged from contact point 1 while increasing portions ofresistance a are inserted between center tarp c and contact point 2.Simultaneously, decreasing resistance of portion b appears betweencenter tap c and contact point 3. Thus, a uniform transition ofresistance values is obtained as the resistive slider element 32 movesalong successive increments of the main potentiometer winding 14.

It will be readily apparent to those skilled in the art that the utilityof the invention is not limited to resistance type voltage dividers, asdisclosed in the preferred embodiment, but that the resistive contactorof the invention may be employed to derive smoothly changing monotonicvoltage variations, as a function of relative motion, from a multipletap electrical transformer, or from any other source of multiplepotential values. Thus, for example, the coil 14 shown schematically inFIGURE 4 and FIGURE 5 of the drawing may be a transformer winding, orthe separate taps such as l, 2 and 3 in. FIGURE 5 may be connected todifferent cells of a multicell battery potential source, if desired.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efiiciently attained and,since certain changes may be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention which,as a matter of language, might be said to fall therebetween.

Having described my invention, what -I claim as new and desire to secureby Letters Patent is:

1. Variable electrical resistance apparatus comprising, in combination,a first resistive element of predetermined fixed resistance value andhaving the resistance thereof distributed over an exposed surface area,a second resistive element of a different predetermined resistance valueand having the resistance thereof distributed over a lessersubstantially contiguous surface area, means establishing electricalconductivity between the exposed surface area of said second element andat least a portion of the exposed surface area of said first element,means establishing an external electrical connection to a centralportion of said second resistive element, and further means enablingrelative motion between said first and second elements whereby theexposed distributed resistive portion of said second element may bebrought into conductive engagement with successive portions of theexposed resistive surface area of said first element.

2. The combination of claim 1 in which the total distributed resistanceof said second element is of a value at least twice the resistance ofthe corresponding portion of said first element in conductive engagementwith said second element at any given time, regardless of relativemotion between said first and second elements.

3. The combination of claim 1 in which said first resistive element isadapted for stationary mounting and said second resistive element ismove-ably mounted with respect thereto for conductive engagement withsuccessive portions thereof.

4. The combination of claim 1 in which said first resistive elementcomprises a toroid of resistance wire wound upon a substantiallycylindrical member of insulating material with an annularly disposedsubstantially plane surface of said toroid being exposed for conductiveengagement with the distributed resistive portion of a rotatable secondresistive element.

5. Monotonic voltage dividing means comprising, in combination, asubstantially unifomly distributed fixed resistance element formed ofsubstantially homogeneous resistance material, an uninterrupted surfaceportion of said resistance material being exposed for conductiveengagement with a plurality of voltage taps, means establishingsimultaneous conductive engagement between different portions of saidexposed surface and a plurality of different potential taps, furthermeans establishing electrical connection to a center portion of saidresistance material, and means for imparting relative motion betweensaid resistance element and the engaging potential taps whereby thevoltage potential appearing at said further connection means representsa continuous average of the potential appearing at adjoining voltagetaps in conductive engagement with said resistance element.

6. A slidably moveable wiper contact member for variable potentialdividing devices comprising, an element of constant resistance materialhaving a substantially uniformly distributed electrical resistance valuethroughout, a substantially uninterrupted surface portion of saidmaterial exposed for electrically conductive engagement with a pluralityof adjacent potential conducting members, and means establishing anexternal electrical connection to a centrally disposed portion of saidresistance element.

7. A noise free linear potentiometer, substantially as described,comprising in combination, a first resistance element adapted for theapplication of a differential voltage thereacross, said first resistanceelement having an elongated exposed surface area, the resistance perunit length in the direction of said elongation of said first resistanceelement being substantially constant over said exposed surface areawhereby a linear voltage continuum is established over said exposedsurface area when a differential voltage is applied across said firstresistance element, a second resistance element adapted for slidableengagement with a relatively small area of said elongated exposedsurface area of said first resistance element, the resistance per unitlength of the contacted surface area of said second resistance elementin the direction of said elongation being more than twice that of theresistance per unit length of said exposed surface area of said firstresistance element, a low resistance tap to a point in said secondresistance element, said point being spaced from said contacted surfacearea along a line perpendicular to a plane tangent to said contactedsurface area at the center of gravity of said contacted surface area,whereby when a differential voltage is applied across said firstresistance element and said second element is slidably moved along saidelongated exposed surface area of said first resistance element in thedirection of said elongation the voltage produced at said tap is alinear function of the position of said second resistance element withrespect to said first resistance element and is relatively unaffectedwhen small areas of said surfaces are separated by impurities andsurface discontinuities.

8. Variable electrical resistance apparatus comprising, in combination,a toroid of resistance wire wound upon a member of insulating materialforming a first resistive element of predetermined fixed resistancevalue and having the resistance thereof distributed over an exposedsurface area, a substantially uniformly distributed helical winding ofresistance wire mounted upon a rotatable arm of insulating materialforming a second resistive element of a different predeterminedresistance value and having the resistance thereof distributed over alesser surface area, an annularly disposed substantially plane surfaceof said toroid being exposed for conductive engagement with thedistributed resistive portion of said second resistive element, meansestablishing electrical conductivity between the exposed surface area ofsaid second element and at least a portion of the exposed surface areaof said first element, means establishing an external electricalconnection to a central portion of said second resistive element, andsaid arm being rotatably mounted in the axis of said toroid whereby saidwire-wound second resistive element may be progressively rotated intosuccessive engagement with substantially all portions of the exposedplane surface area of said first resistive element.

9. Variable electrical resistance apparatus comprising, in combination,a first resistive element of predetermined fixed resistance value andhaving the resistance thereof distributed over an exposed surface area,a second resistive element of a different predetermined resistancevalue, said second resistive element being a substantially homogeneousmember formed of resistance material selected from the group includingrhodium, beryllium, titanium, chromium, and alloy mixtures thereof, theresistance of said second resistive element being distributed over alesser surface area, means establishing electrical conductivity betweenthe exposed surface area of said second element and at least a portionof the exposed surface area of said first element, means establishing anexternal electrical connection to a central portion of said secondresistive element and further means enabling relative motion betweensaid first and second elements whereby the exposed distributed resistiveportion of said second element may be brought into conductive engagementwith successive portions of the exposed resistive surface area of saidfirst element.

10. Variable electrical resistance apparatus comprising, in combination,a first resistive element of predetermined fixed resistance value andhaving the resistance thereof distributed over an exposed surface area,a second resistive element of a different predetermined resistancevalue, said second resistive element being a substantially homogeneousmember formed of a compound in which carbon is the principal ingredient,the resistance of said second resistive element being distributed over alesser surface area, means establishing electrical conductivity betweenthe exposed surface area of said second element and at least a portionof the exposed surface area of said first element, means establishing anexternal electrical connection to a central portion of said secondresistive element, and further means enabling relative motion betweensaid first and second elements whereby the exposed distributed resistiveportion of said second element may be brought into conductive engagementwith successive portions of the exposed resistive surface area of saidfirst element.

11. An infinite resolution potentiometer, comprising in combination, afirst resistive element of predetermined fixed resistance value andhaving anexposed surface area substantially extending from oneelectrical end thereof to the other, said first resistive elementadapted to be connected across a source of electrical potential, asecond resistive element of a diiferent predetermined resistance valueand having a substantially contiguous surface area thereof exposed forelectrically conductive engagement with at least a portion of theexposed surface area of said first element, means establishing anexternal electrical tap near the electrical center of said exposed areaof said second resistive element, and means for establishing electricalconductive engagement between the exposed surface areas of said firstand second resistive elements and for enabling relative motion betweensaid first and second resistive elements, whereby when said firstresistive element is connected to a source of electrical potential andsaid second resistive element is moved relative to and in electricalconductive engagement with said first resistive element a substantiallysmoothly varying potential is produced at said external electrical tap.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Zeitschrift fiir instrumentenkunde, vol. 34, 1914, page 149.

